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Building Tips and technical articles. => 1/2 A building. => Topic started by: minnesotamodeler on March 10, 2008, 08:23:42 PM
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Some time back John posted a thread about his "Green Giant" with diamond airfoiled ribs, no spars, to allow the covering to sag between ribs. With his permission I have borrowed the concept--here's the wing so far.
The concept is simple: Thick airfoil at the ribs, sagging to a thinner curved cross section between. The ribs are 1 1/2" tall; with 6" avg. chord that makes a 25% airfoil--but it sags between (ribs are at 3" spacing to allow) to a minimum of 3/4", 12.5%. I included an interior spar, 3/4" tall, to limit the sag. Average airfoil somewhere between, probably 15-16% or so. Cut a cross section betweeen the ribs and you'd see the covering assumes a curved, standard airfoil shape.
Advantages that I can see include quick easy cutting-out of ribs with minimal waste, and foolproof build since it lays flat on your building board. No chance of warps. No jig needed; your building surface becomes the jig. Just hope it flies well!
Also I included a few shots of the bellcrank mount--the center post is a length of clotheshanger wire; spacers to center the BC are 1/4" lengths of fuel line. Center planking goes over the post to hold it in. I offset the BC to the outboard to clear the pushrod; see the last few pics.
A big thank-you to John for the idea. Flight reports this Spring. If it ever gets to MN.
--Ray
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Hey Ray, thats looking good. You sure do cut nice clean and even pieces, mine are always marked up and have jagged edges in the cut out areas.
How are you going to finish the tail? To me its begging for twin booms.
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Kind of a cross between mono-boom and whaletail. It'll look a little like this: Except the tail will be smaller. This one was sort of overkill.
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Looks to me like you took earlier posts to heart Ray..........I mean the posts where the guys asked why you used a ply BC and wooden dowel for a BC peg. It's a good way to keep from having to explain. y1
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Looks to me like you took earlier posts to heart Ray..........I mean the posts where the guys asked why you used a ply BC and wooden dowel for a BC peg. It's a good way to keep from having to explain. y1
Don't getcher hopes up too far, Frank, I don't learn that easy...ply. bellcranks still go in those planes that need slow controls (my trainers, the SkyWriter, LittleAxe, etc.) 'cause I can make 'em 3" LO to LO without going to a huge, heavy commercial bellcrank made for a big plane. My 1/8" thick ply. BC weighs negligible-y. and 1/8" wooden dowel with it because it needs more bearing area.
I used a wire post on the commecial 1/2A bellcrank you see in the pics, because it's a perfect slip fit without any boring out, or honing the wire down, or any of that nonsense. I was checking coat hangers for the closest and happened upon one that was perfect.
I am unreformed and unrepentant.
Note the continuous leadout wire threaded through the bellcrank, LO police notwithstanding. "Come and get me, coppers!"
--Ray
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Just to keep the thread up to date, here's pictures of the complete airplane in bones, ready to cover. As it sits, just under 2 oz. --with engine, tank & covering, I figure about 5 oz. RTF.
I did a little something different at the elevator horn/pushrod attachment, see 3rd pic. Just a wheel collar on a straight pushrod, with1/4" long set screw through the horn. Infinitely adjustable, no bends.
pic #4 shows the over/under LO guides I've been using for awhile.
Pic #5, angled blocks for engine offset--cut from the ends of a wooden spring-type closthespin.
Pic #6, the semi-monoboom/maybe-whaletail attachment: Center section planking extends over the TE, with a 1" wide notch the tail sits in, flush with the planking. One each top and bottom, laminated together behind the TE. Light and strong.
--Ray
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Please schedule mine for delivery by 4/05/08 !! Set-up for Norvel and internal bladder if possible. H^^
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Please schedule mine for delivery by 4/05/08 !! Set-up for Norvel and internal bladder if possible. H^^
Say Ray, happy to do it, but this is an entirely experimental airfoil. You probably want this one, tried and proven:
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Looking good MM. 2 oz :o ! You da man. Whats the wingspan on that rascal? I'm a big fan of power, but an .061 is gonna be way too much at that weight. My recent stick plane weighs 8 oz and with an AP 061 I have to fly it on 45' lines minimum, just too fast. A Norvel or TeeDee 049 should be more than enough for your plane. You gonna use a pressure bladder or ballon tank?
Hey Ray Copeland, how things over in McCleansville? I went flying today over at Alamance Elementary, my sons school (just finished repairing the damage n~ ). Theres a nice concrete pad to take off from and a good field to fly over. We gotta get together sometime and fly, if work will ever let me stay home for more than a day or so.
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Looking good MM. 2 oz :o ! You da man. Whats the wingspan on that rascal? I'm a big fan of power, but an .061 is gonna be way too much at that weight. My recent stick plane weighs 8 oz and with an AP 061 I have to fly it on 45' lines minimum, just too fast. A Norvel or TeeDee 049 should be more than enough for your plane. You gonna use a pressure bladder or ballon tank?
Hi John, 30" span, 190 sq. in., 5 oz. or so. Yes, an .049 will fly it fine, but It's really designed with that .061 in mind--flying one with that much power is a real blast! Certainly, 42' lines minimum. It's a combat plane after all, you just gotta be fast to keep up with it, it's part of the whole "combat experience". And at that speed (75 mph or so, 2-sec. laps on 35' lines, don't try it--2.5 sec. laps on 42', more do-able) and quickness of turn, a pressure bladder is a necessity. Any other fuel system will starve out in turns.
It is great to fly a plane that goes where you point it RIGHT NOW, gets there before you do unless you anticipate it. No real purpose to it, it'll never be in a fight 'cause no-one uses built-up wings any more, they just buy disposable foamies mass-produced in Russia or China or somewhere; but it's just plain fun to get hold of a hi-performance plane like this that you built yourself and, as they say, punch holes in the sky for awhile. End of commercial.
--Ray
http://snipurl.com/9igp
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To return to the "saggy diamond": Here it is half-covered, showing the sag--less than anticipated, 1.5" at ribs, about 1" between; from 25% airfoil to 16% or so--average 20%, more than I wanted. Ribs will have to be shallower on the next one, maybe 1.25" or so.
--Ray
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Just space them futher apart. That would lighten it up also. LL~
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Just space them futher apart. That would lighten it up also. LL~
Yes, that's actually a possibility, no joke...they're 3" OC now, with a short bay next to the center section. Maybe go to 3.5" and eliminate that short bay. I wonder how much additional sag that would induce.
--Ray
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OK, big update...I flew the droopy diamond airfoiled Rumbler today...One word: WOW! I thought it would be slower than the round-airfoil version; I thought wrong. With my Norvel .061 and a 5.7x3 APC prop, clocked it at 2.4 sec./lap on 42' lines, do the math, that's 75 mph! I was amazed.
But more than that, the turns were even more amazing. Turns so quick it seems to pick up speed in maneuvers...what a blast, just flashes all over the sky. Tight consecutive loops with no bogging; change of direction so fast it almost seems to disappear. I "lost" it a couple of times when it jumped out of my vision field quicker than I anticipated. Yeah, I'm old and slow but do know how to fly combat wings.
Anyhow, I am tickled pink with it. Hoped it would fly well; had no notion it would be this good. I flew it many times until I finally stuck it in good--lost it over the top behind my back when it moved faster than I could again. No major damage, well, outboard wing cracked the LE and broke one rib; and the stab split. So it's tough too!
"Needless to say", I'm not slimming down the airfoil after all as I thought I might. Many thanks to John Crocker for turning me on to this airfoil. I'll show pics of another when I get it built. Also I smell another kit offering soon.
--Ray
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Glad to hear it is working. Looking at the photos it looks like a thick flat plate with the ribs looking like wing fences. If you do a kit let me know. DOC Holliday
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Have to say it 'TOLD YOU SO" n~
Thought of something else on this. When I covered the Confederate Twin, I used Econocote which is lighter and shrinks up more than Monocote. May want to try it to get a deeper draw.
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Say it again, John...say it loud! you deserve the satisfaction.
At this point, I'm mighty happy with it the way it is! I do intend to space the ribs out another 1/2" or so per bay, to eliminate one more rib as much as anything else; that may increase the "draw" (like that term) a little. I also may give the Econocote a shot, I have enough of a roll to do one I think.
Doc, between the ribs it assumes a "normal" curved-airfoil cross section--I think that's the key to its success, along with the "wing fence" effect you mention. All I know for sure is, it works, and works well!
A kit looks likely, I'll let you know.
--Ray